Method and device for proctecting a reading device for card-shaped data carriers from unauthorized evaluation or copying of magnetically encoded data of an inserted card-shaped data carrier

ABSTRACT

The invention relates to a method and devices for protecting a reading device ( 1 ) for card-shaped data carriers ( 2 ) against unauthorised evaluation or copying of magnetically encoded data detected in the reading device ( 1 ) for card-shaped data carriers ( 2 ). To this end, an electromagnetic noise field ( 18 ) is generated by means of a noise field coil ( 17 ). The use or disposition of the at least one noise field coil ( 17 ) is such that the authorised magnetic field reading head ( 10 ) is also affected by the noise field ( 18 ) of the noise field coil ( 17 ) when the magnetically encoded data of a card-shaped data carrier ( 2 ) is being read. An output or sum signal of the authorised magnetic field reading head ( 10 ) generated from the wanted signal of a card-shaped data carrier ( 2 ) and from the effects of the noise field ( 18 ) is detected. The effect of the noise field ( 18 ) of the noise field coil ( 17 ) in the output or sum signal of the authorised magnetic field reading head ( 10 ) is then compensated or filtered out or the wanted signal is selectively filtered out of the output or sum signal of the authorised magnetic field reading head ( 10 ).

The invention relates to methods and devices for preventing unauthorisedand unnoticed evaluation or copying of information stored on card-shapedmagnetic data carriers, as defined in claims 1, 14, 24 and 26.

Particularly in connection with cash cards, situations repeatedly arisewhere cash dispensers or similar service machines which are equippedwith reading devices suitable for such cash cards are manipulated byunauthorised third parties with malicious intent so that when thesemachines are used as intended by a user in good faith, the data recordedon the magnetic stripe of the card-shaped data carrier is read unnoticedwith a view to criminal intent. To this end, an additional reading headis unobtrusively fitted on the opening into which the magnetic card isintroduced, which then detects the data stored on the card unnoticedwhen it is introduced. This data is then stored and misused subsequentlyto make a copy of the card containing identical data. In the situationwhere a PIN code is needed, it is usually filmed or observed as it isentered on a user terminal. This information is then used by criminalsin conjunction with a copy of the card for fraudulent purposes.

In the case of reading devices used in cash dispensers, therefore,structural features have been used in the region of the card readeropening in some cases, in particular devices fitted in front of thecard-reader slot, or complex and expensive monitoring systems have beeninstalled with a view to making it more difficult to fit additionalreading devices. These features are satisfactory but only under certainconditions.

A system is also known from document DE 20 2005 021 134 U-1, whereby amagnetic noise field is generated in the region of the introductionorifice of a card reader so that detection of the card data via areading head illegally fitted in this region is disrupted. As a result,the data cannot be read, recorded and reproduced to enable an identicalor usable clone of the original card to be made. In the case of thisknown system, a magnetic coil is mounted in the region of the cardreader opening, which is fed by an appropriate frequency generator sothat a magnetic noise field is generated in the region of the cardreader opening and disrupts the operation of a reading head fitted witha view to manipulation. The main disadvantage of this known system isthat the magnetic noise field of the coil not only disrupts a readinghead fitted in front of the card reader opening with criminal intent, italso interferes with the reading head of the actual card reader. Inpractice, this problem is currently being dealt with by opting for cardreaders of a relatively deeper design in which the reading head in theinterior of the card reader is spaced that much farther back from thecard reader opening. Furthermore, the noise field is switched off assoon as an inserted card has disappeared completely in the card readerand is therefore outside the detection range of a reading headpositioned outside the card reader that has been fitted for criminalpurposes. However, it is only possible to use these features with alimited number of card readers of a sufficiently deep design, especiallyin the case of card readers where the card disappears completely in thereader opening before the magnetic stripe of the card reaches theinternal or legitimate reading head. Particularly in the case of cardreaders of a shorter design used by preference for access systems inwhich the internal legitimate reading head is disposed relatively closeto the card reader opening, such deterrents are not possible. Especiallyin the case of PDQ readers or swipe readers, these precautionaryfeatures are usually totally futile.

The objective of this invention is to propose methods and devices bymeans of which the unauthorised detection of magnetically encoded dataon card-shaped data carriers in the region of reading devices can bereliably prevented for these data carriers, offering a high degree ofsecurity against attempts at manipulation.

Independently of the above, another objective of this invention is topropose a system whereby the effect of the noise field can be filteredout of the output or sum signal of an intercepting illegal reading headby simple means.

Related to the above objectives, another independent objective of theinvention is to propose features whereby fraudulent tampering in thevicinity of the reading device can be reliably detected.

The first of the above-mentioned objectives of the invention is achievedby the features specified in claim 1 or 14.

The advantage of this approach is that a reading device operated orworking on the basis of this method offers increased security againstfraudulent tampering. Specifically, amongst other things, the noisefield no longer has to be deactivated as the magnetic data carrierpasses through the internal or authorised magnetic field reading head ofthe reading device. In particular, the noise field can remain activated,even during the phase of reading information or data contained on thedata carrier, because the effect of the noise field can be compensatedat any time using signal technology. It is therefore possible to use anelectromagnetic noise field with reading devices of a relatively shortdesign. In particular, the data of the data carrier can already be readwhilst a portion of the card-shaped data carrier is still projecting outfrom the reading device and a fraudulently fitted reading head is stillaccessible under certain circumstances. This means that the deterrentsproposed by the invention can also be used without any problem inconjunction with reading devices with a short, automated transportdistance for the card-shaped data carrier and also with what arereferred to as PDQ readers or swipe readers where the data carrier isintroduced manually or by a relative movement. An illegally fittedreading head is therefore subjected to the noise field at every relevantinstant without the possibility of compensation based on signals forthis illegally fitted reading head, thereby reliably preventing anyunauthorised detection, evaluation or copying of relevant useful data.

The advantage of the feature defined in claim 2 is that the suppressedwanted signal which is derived from the magnetic field of thecard-shaped data carrier, is restored by computing or digital signalprocessing, thereby resulting in a particularly rapid and reliable oraccurate reconstruction of the wanted signal. The essential aspect isthat using the model based on signals, the effect of the noise field canbe computed for any and every characteristic of the noise field and forrandom and virtually random characteristics of the noise control signalsupplied to the noise field coil. By contrast with the system of using aperiodic noise signal as is the case in the prior art, using a virtuallyrandom noise control signal means that it is no longer possible toreconstruct the undisturbed signal elements solely from the signal ofthe illegally fitted reading head, i.e. the suppressed wanted signalelements. Fraudulent tampering and attempts at detection for thispurpose will therefore no longer enable data or information to beobtained from the relevant card.

The features defined in claim 3 ensure that the effect of the magneticnoise field can also be detected in the output signal of the authorisedmagnetic field reading head, which means that both the presence inprinciple as well as any changes to the noise field can be detected.

Based on another advantageous embodiment defined in claim 4, astochastic, i.e. a random noise control signal or noise field with arandom time sequence is used. Whilst it is possible to filter out theeffect of a periodic noise signal on the signal of an illegally fittedreading head relatively easily, thereby enabling the non-distortedsignal information to be reconstructed, this is no longer possible ifusing a quasi-random noise control signal.

As a result of the features defined in claim 5, a noise control signalwhich has good stochastic properties is generated in a practical manner.This means that even in the event of a long-term recording of the signaldelivered by an illegally fitted, intercepting reading head created byadditive superimposition of the noise field and the useful data of themagnetic stripe, it is no longer possible to obtain processable signalsor information or data which could otherwise be misused to clone thecard.

The features defined in claim 6 also enable the use of stochastic noisecontrol signals or noise fields and these noise effects based on anabsence of rules can be compensated again exclusively by the integralsignal processing inside the reading device. What is available to quasiexternal or illegal magnetic field reading heads, on the other hand, isa mixed form derived from the noise field and the magnetic field of thedata carrier and it is not possible to split or separate the respectivesignal elements without having a knowledge of the characteristic of thestochastic noise control signal.

The advantage of the features defined in claim 7 or 8 is that it can becalculated in advance, as it were, what an emitted noise control signalwill look like or how it will have been changed after having beentransmitted across the transmission distance and picked up again. As aresult, it is possible to generate any signal shapes, transmit themacross the transmission distance and then compute the noise signalelements or noise effects of the noise control signal and reconstruct awanted signal corresponding to that which would otherwise have beendetected without the effect of a noise field. In particular, this meansthat the signal distortions in the output or sum signal of the internalor legal magnetic field reading head can also be totally eliminated ifcomplex, and in particular stochastic, noise control signals aretransmitted.

As a result of the feature defined in claim 9, it is also possible toset up particularly complex transmission characteristics. The essentialaspect of this is that the model filter can be adapted so exactly to thereal transmission behaviour, and virtually the identical signal isobtained at its output as at the output of the authorised magnetic fieldreading head, and a corresponding sequence of scanning values appears atthe output of an AD converter connected downstream if no card-shapeddata carrier is being read, in other words only the noise field isacting on the authorised magnetic field reading head. On the basis ofsimple subtractions, therefore, the noise signal can be removed from atotal or sum signal of the magnetic field reading head and the remainingsignal processed further as a reconstructed wanted signal.

Due to the features defined in claim 10, there is no risk at any timethat the useful signals or data of the data carrier can be detected onan unauthorised basis. In particular, there is no time window in whichit would be possible to obtain a quasi-pure signal from the data carrierwith the magnetically encoded data. Security against fraud and tamperingis improved to a high degree as a result.

The advantage of the features defined in claim 11 is that fraudulentmanipulation or also time-dependent or age-related defects can bedetected on an automated basis. One advantage of this solution, amongstother things, is that if magnetically and/or electrically conductiveparts are fitted, removed or tampered with in the range of the noisefield coil, the magnetic field lines and transmission behaviour of thenoise field coil are changed on the internal magnetic field reading headof the reading device. At the same time however, and above all, avariable is available with a signal-based model to enable the originalstate to be compared with the desired state. This means that thepreviously emitted signal-based model will no longer match the real oractual transmission conditions which occur if magnetically active partshave been illegally fitted or modified within the range of the readingdevice or its noise field coil, or are removed from within this range.With effect from a specific quantity, this variance may be evaluated asan indication that there has been fraudulent tampering and the readingdevice or some other peripheral unit, in particular a cash dispensingmachine fitted with it, can be immediately taken out of service and analarm triggered if necessary. The same applies in the case of a simpletechnical defect which changes the effect or behaviour of thetransmission link. This might be the case in the event of a change tothe characteristic of the noise field coil or the internal, authorisedmagnetic field reading head, for example. A technical defect of themagnetic field reading head of the reading device can also beautomatically detected and reported as a result of these features.

The advantage of the features defined in claim 12 is that the digitalfilter can continue to be adapted at a fast adaptation speed, even afteran initial calibration routine or after an initial setup. This meansthat the filter coefficients of the signal-based model can also beautomatically adapted to a slowly changing transmission behaviour. Evenwithout attempts at tampering, slight or creeping changes can occur inthe transmission behaviour during normal operation. These might becaused by temperature-induced or age-related changes to componentvariables, for example. Continuous adaptation of the model filterensures that even in the event of slight changes to the transmissionbehaviour, the effect of the noise field on the magnetic field readinghead of the reading device can always be optimally compensated and thenoise field cannot cause any impairment to reading quality. It is alsoof particular advantage to use a stochastic test signal for adapting themodel filter, which effectively covers the requirements involved inpreventing unauthorised detection attempts.

The advantage of the features defined in claim 13 is that reconstructionof the wanted signal based on the signal of an illegally fitted magneticfield reading head is made even more difficult. In particular, thisadditional signal component also makes it more difficult to distinguishor single out the wanted signal originating from the data carrier on thebasis of signal processing. Unauthorised detection attempts whereprocessing of the detected signal relies on detecting specific, typicalsignal shapes are therefore reliably prevented.

The objective of the invention is also achieved by means of a device asdefined in claim 14.

The advantages and effects which can be achieved with this deviceessentially mirror the advantages and effects specified in connectionwith the features used for the method defined in claim 1. In particular,the effect of the noise field coil on the magnetic field reading head ofthe card reader can be compensated at any time as a result and theactual wanted signal originating from an inserted card-shaped datacarrier can therefore be reliably extracted. This enables the noisemagnetic field to be continuously maintained and allows the use of morecomplex noise control signals whilst offering a more compact design ofthe reading device. The particularly high security with regard to fraudand tampering in the case of a reading device equipped in this mannercan also be easily achieved on existing reading devices. In particular,existing devices can be retro-fitted and updated relatively free ofproblems. In addition, the internal, authorised noise field compensationoperates particularly reliably and can also be used for complex anddata-intensive signals without any extra delay or processing times.

The embodiment defined in claim 15 ensures that without a knowledge ofthe characteristic of the noise control signal, it is no longer possibleto extract the actual wanted signal. The random noise control signaltherefore makes it more difficult to detect any useful information whichcan be processed and thus thwarts fraudulent interception. This can bemade even more difficult by opting for a multiple array, in particular adouble array, of noise field coils, each with linearly independent noisecontrol signals.

The advantage of the embodiment defined in claim 16 is that, byrestricting or concentrating the bandwidth of the noise control signalto or within the range typical for the wanted signal, the total power ofthe noise control signal can be reduced as a ratio of its power oreffect in the frequency range of the wanted signal. Conversely, thismeans that whilst maintaining a constant or specific output power of thenoise field, a stronger effect can be obtained in the spectral range ofthe wanted signal. The amplifier stages as well as the noise field coilcan therefore be rated for a lower power which, as a rule, means that acompact design and energy-saving operation can be obtained.

The advantage of the design defined in claim 17 is that the essentialparts of the signal processing take place in digital format. Inparticular, the noise signal computed by means of the signal processorand reproduced on the basis of the model can simply be subtracted fromthe output or sum signal of the magnetic field reading head and theremaining wanted signal can either be converted back into an analoguesignal by a DA converter and made available for continued processing orthe wanted signals is already evaluated by software in the signalprocessor. This guarantees an inexpensive overall solution and the noisefield generator proposed by the invention is integrated in the controland evaluation electronics of the card reader.

As a result of the embodiment defined in claim 18, the effect of thenoise field can be calculated sufficiently accurately in advance. Thismay be easily implemented using software and converted by means of asignal processor. A digital filter of this type is characterised by aset of filter coefficients by means of which the exact frequency andphase response of the filters can be set. Also of advantage is the factthat a signal-based model of this type can be easily and rapidly adaptedto changing conditions or to legitimately changing circumstances orsituations by simple reprogramming or recalibration and, if necessary,can even be so during ongoing operation.

The advantage of the embodiment defined in claim 19 is that the filtercoefficients, preferably determined as part of a calibration routine,can be stored on a non-volatile basis in a memory, so that when thenoise field generator or reading device is switched on again, there isno need for another calibration routine.

The advantage of the embodiment defined in claim 20 is that a set ofreference coefficients is available, which describes the transmissionbehaviour of the legitimate, non-manipulated state of the readingdevice. The filter coefficients of the model filter can be adapted atleast once as part of a calibration routine so that the transmissionbehaviour of the signal-based model corresponds to that of the realsignal path across the noise field coil.

The advantage of the features defined in claim 21 is that the storedmodel parameters are used as comparison values for evaluating thepresence of tampering or defects of the reading device. In this case,therefore, it is not the remaining noise signal which can no longer befully compensated that is used as an indication of tampering or a defectbut the variance of the continuously or periodically calibrated modelparameters compared with the originally determined and stored parameterswhich is used as an indication of tampering or a defect. For example,this enables automatic detection of fraudulent tampering in the vicinityof the reading position for a card-shaped data carrier, in particular inthe region of the slot through which a card-shaped data carrier isinserted. Criminal attempts to get round the system in the form ofelectromagnetic screening or shifting of the noise field coil, thesefeatures being intended to reduce or eliminate the effect of the noisefield coil on the illegally fitted reading head, can be automaticallydetected. A defect or a deliberate action to switch off the function ofthe noise field coil is automatically detected as a result.

The embodiment defined in claim 22 results to a certain extent in amulti-channel noise field, thereby further reducing the possibilities ofreconstructing the wanted signal corresponding to the card data from thesignal of an illegally fitted reading head. In particular, the securitypreventing tampering with such a reading device is improved.

As a result of the embodiment defined in claim 23, sufficiently smallmanufacturing tolerances will result in very constant transmissionbehaviour and readily reproducible noise field effects. Consequently,the signal-based model provided as a means of compensating the effect ofthe noise field is of a standard design suitable for all and many typesof reading devices. In many cases, this obviates the need for an initialadaptation or the setting of model parameters based on examples.

The embodiment defined in claim 24 results in a reading device whichoffers a particularly high degree of security against manipulation andtampering.

The advantageous embodiment defined in claim 25 automatically prevents arightful owner or user from inserting a card-shaped data carrier ifnon-typical situations or situations indicating tampering occur. Thisspecifically prevents any relative movement between a card-shaped datacarrier and an illegally fitted reading head.

Finally, an embodiment defined in claim 26 is of advantage becauseautomated teller machines such as cash dispensers or automated transfermachines, or access control systems are proposed which offer a highdegree of security against tampering and fraud.

Also of advantage are the additional features defined in claim 27because the data on the magnetic stripe to be protected is at no pointinserted in the reading device or placed in the transmission path to thehigher-ranking electronic unit so that it could be or read or accessedby illegally fitted electronic circuits or changes made to the originalhardware or software.

The features defined in claim 28 are also of advantage becausecomprehensive protection can be obtained against fraud and tamperingusing relatively simple hardware. In particular, the data of themagnetic stripe is encrypted in the same unit as that in which the noisefield is compensated. This is a relatively smaller range which is wellprotected from the outset and which cannot be accessed other than with alot of effort and only with very specialised technical know-how.

The invention will be explained in more detail below with reference toexamples of embodiments illustrated in the appended drawings. These arehighly simplified, schematic diagrams illustrating the following:

FIG. 1 illustrates an example of a reading device of the type based on areader which draws in card-shaped data carriers, corresponding to thesystem known from the prior art;

FIG. 2 shows the card reader illustrated in FIG. 1 in a state in whichit has been tampered with for fraudulent purposes, a well-meaning userof the reading device usually being unaware of such tampering;

FIG. 3 illustrates a reading device protected against tampering asproposed by the invention, on which an additional reading head of thetype illustrated in FIG. 2 has been fitted for fraudulent purposes;

FIG. 4 shows an embodiment of the design illustrated in FIG. 3comprising more than one noise field coil;

FIG. 5 is a block diagram of the signal processing unit, such as may beused to implement the invention;

FIG. 6 is an extended signal processing unit incorporating an adaptive,signal-based model;

FIG. 7 illustrates an embodiment of the signal processing unitincorporating a multiple array of adaptive, signal-based models andadditional, integral evaluating units as well as control andcommunication interfaces;

FIG. 8 shows a technical design of the reading device protected againsttampering.

Firstly, it should be pointed out that the same parts described in thedifferent embodiments are denoted by the same reference numbers and thesame component names and the disclosures made throughout the descriptioncan be transposed in terms of meaning to same parts bearing the samereference numbers or same component names. Furthermore, the positionschosen for the purposes of the description, such as top, bottom, side,etc., relate to the drawing specifically being described and can betransposed in terms of meaning to a new position when another positionis being described. Individual features or combinations of features fromthe different embodiments illustrated and described may be construed asindependent inventive solutions or solutions proposed by the inventionin their own right.

FIG. 1 illustrates a conventional reading device 1 for card-shaped datacarriers 2, on which information or data is at least magneticallystored. In particular, this reading device 1 is designed to processmagnetic cards 3 with at least a magnetic stripe 4 and/or chip cardswith at least a magnetic stripe 4. In a manner known per se, datarelevant to usage and security is stored on this magnetic stripe 4,which can be automatically read and/or edited or updated by the readingdevice 1. Such card-shaped magnetic data carriers 2 might be bank cardsor cash cards in particular, as well as authorisation cards used forauthentication purposes in connection with access or usage authorisationfor specific facilities. In other words, the specified reading device 1is often used in bank or other service-related automated machines oraccess control systems.

Such reading devices 1 usually comprise the following components: ahousing 5, at least one insertion orifice 6 or card reader opening inwhich magnetic data carrier 2 is inserted and then subsequently removed,usually at least one motor driven conveyor roller 7, 7′ forautomatically drawing in and pushing out an inserted data carrier 2,optionally counter-pressure rollers 8, 8′ and/or guide elements 9, atleast one magnetic field reading head 10 for detecting by sensingmagnetically encoded information stored on the data carrier 2 and anevaluation and control circuit 11 for controlling the relevant functionsof the reading device 1 needed for the reading operation and fordecoding the signals delivered by the magnetic field reading head 10and/or by an array of spring elements for contacting the chip and/or bya contactless reading unit or RFID module. The evaluation and controlcircuit 11 is usually also used to convert the detected signals intocorresponding digital information and to forward this information via anappropriate signal and data interface 12. The data interface might be aninterface permitting a two-way exchange of data, such as a serialinterface (RS 232, RS 485), an Ethernet or USB-interface. The signal anddata interface 12 may also comprise nothing more than one or more statusor signal wires 13 across which specific statuses can be signalled. Sucha status and signal wire 13 might be used to unlock an access door whenan inserted data carrier 2 is recognised as being valid and authorised,for example.

The diagram of FIG. 1 illustrates a magnetic card reader, in which aco-operating magnetic card 3 with a magnetic stripe 4 has been partiallyinserted. The evaluation and control circuit 11 is illustrated outsidethe housing 5 of the reading device 1 to provide greater clarity.However, the evaluation and control circuit 11 is usually integrated inthe housing 5 of the reading device 1 together with the mechanical andelectrical components.

With a view to retaining greater clarity, other generally standardmechanical, electrical and electromechanical components of a card readerwhich are not necessarily crucial to the invention have been omittedfrom the drawing, for example a flap or shutter on the card readeropening which can be electro-mechanically locked, spring-biased pressingand guide elements, a voltage supply, sensors for detecting and definingthe position of an inserted data carrier 2, memory elements for storingand retrieving data and programmes by a processor unit (CPU, DSP), aswell as various signal-based links. These elements are also well knownfrom the prior art and can be readily inferred and implemented by theperson skilled in the art.

FIG. 2 illustrates a reading device 1, in particular a conventionalmagnetic card reader of the type illustrated in FIG. 1, on which anothermagnetic field reading head 14 has subsequently been fitted in front ofthe actual card reader opening or in front of the insertion orifice 6for a card-shaped data carrier 2 by a criminal for fraudulent purposesso that when a magnetic card 3 is inserted, the information or datacontained on it can be intercepted and used subsequently to make anillegal copy of a magnetic card containing the same data. Due to what isusually a very compact and inconspicuous design, the additional,magnetic reading head is not usually perceptible as being such and thecard information can be unlawfully detected without the authorisedcardholder realising it.

The signal of the additionally fitted, illegal magnetic field readinghead 14 can then be fraudulently recorded—in a manner known per se—bythe criminal on hidden recording apparatus 15 and analysed at a laterpoint in time. As a result, the data obtained in this manner can bemisused to make an unauthorised copy of the card.

FIG. 3 illustrates a reading device 1 proposed by the invention, inparticular a magnetic card reader with an anti-tampering system proposedby the invention or a noise field generator 16 proposed by theinvention. At least one magnetically active noise field coil 17 ismounted on the internal face of the card reader opening or insertionorifice 6, to which a preferably stochastic noise control signal isapplied. The preferably stochastic electric noise control signal on thenoise field coil 17 generates a magnetic noise field 18, which acts on amagnetic field reading head 14 which might have been fitted in front ofthe card reader opening for fraudulent purposes and induces a noisesignal in it which is additively superimposed on the signal generated bya magnetic card 3 as it is moved past. Due to this superimposition ofthe wanted signal on the stochastic noise control signal of the noisefield generator 16 or on the noise field 18 of the noise field coil 17supplied by it, detection of the actual card data is thwarted andunauthorised reproduction of the card data prevented. Furthermore, thenoise field 18 acts in a similar way to the actual magnetic fieldreading head 10 of the reading device 1 in terms of operation. Inparticular, the noise field 18 of the noise field coil 17 may besufficiently intense or the noise field coil 17 and the legal orlegitimate magnetic field reading head 10 may be positioned so close toone another that the noise field 18 also has a significant effect on themagnetic field reading head 10 and its signal behaviour or readingresults.

The noise field coil 17 illustrated in FIG. 3 is shown inside the cardreader opening or inside the housing 5. However, the noise field coil 17may also be mounted in front of the card reader opening in principle, inother words outside of the actual card reader. The noise field coil 17may also be designed as an add-on module which can be retro-fitted.

An equally practical and advantageous embodiment indicated by brokenlines is one based on a structural combination of the magnetic fieldreading head 10 and the noise field coil 17. In other words, it is alsopossible to provide a magnetic field reading head 10 with an integratednoise field coil 17. Such a combination or integration based on lowmanufacturing tolerances offers very constant and readily reproducibletransmission behaviour with respect to the effect of the noise field,and the signal-based model 25 described in more detail below as a meansof compensating for the effect of the noise field may be made to astandard design for all types of machine. In particular, negligiblevariances or scatter can be obtained between the individual types orunits of the magnetic field reading head 10 and noise field coil 17.Accordingly, this obviates the need for adaptation or the setting ofmodel parameters based on examples or at the least this can be reducedto a very simple setup. Alternatively, such an arrangement is alsoespecially well-suited to use with a simple analogue circuit forcompensating the effect of the noise field on the sum or output signalof the magnetic field reading head 10.

The essential factor is that the position of the noise field coil 17and/or a rating of the radiation power, in particular the fieldintensity, or the radiation characteristic, in particular the fieldcharacteristic of the noise field coil 17 and/or a rating of thedetection sensitivity of the authorised respective legitimate magneticfield reading head 10 can be selected so that the noise field 18 of thenoise field coil 17 affects a magnetic field reading head 14 fitted forfraudulent purposes, at least whilst the magnetically encoded data ofthe data carrier 2 is being read, and also acts on the legitimaterespective authorised magnetic field reading head 10 and influences itsoutput or sum signal.

The noise field generator 16 is illustrated as a separate component inthis instance, which may advantageously be designed as an optionaladd-on or expansion module which can be retrofitted on a standard,already existing evaluation and control circuit 11 for a reading device1. In the case of new designs of reading devices 1 above all, the noisefield generator 16 may naturally also be an integral part of the controlelectronics, in particular of the evaluation and control circuit 11.

Signal processing of the noise field generator 16 is based on a digitalscanning system with AD/DA converters 19-19″ at the transitions to theanalogue signals. In order to adapt the respective level of the analoguesignals to the inputs and outputs of the AD/DA converters 19-19′,amplifiers or adaptor stages 20-20″ are provided, which usually alsoincorporate simple low-pass filters (anti-alias filters) and such like.The circuit of the noise field generator 16 also has a digital computerunit, preferably a digital signal processor unit 21 (DSP), which iswired to the magnetic field reading head 10 of the reading device 1, tothe noise field coil 17 of the reading device 1 and to the evaluationand control circuit 11 of the reading device 1. Alternatively, theevaluation electronics may be at least partially provided by the signalprocessor unit 21, as will be described in more detail below.

The noise field generator 16 supplies the noise field coil 17 with astochastic noise control signal, as a result of which the stochasticnoise field 18 is generated. The electric output or sum signal of themagnetic field reading head 10 of the reading device 1, which islikewise affected by the magnetic noise field 18, is then no longer sentdirectly to the evaluation electronics, i.e. is no longer sent directlyto the evaluation and control circuit 11 of the reading device 1 andinstead, is initially forwarded to the digital signal processor unit 21(DSP) of the noise field generator 16, which computes out or filters outall the signal elements correlated with the noise control signal. Thesignal corrected or suppressed by the digital signal processor unit 21,i.e. the wanted signal, is then forwarded to the evaluation and controlcircuit 11 and evaluated in the conventional manner. Alternatively, itwould also be possible for the suppressed signal, i.e. the wantedsignal, to be evaluated by the digital signal processor unit 21 (DSP)and the latter is then used for controlling the sequences of the readingdevice 1 or the peripheral units as well, as will be explained below.

The connection of the reading device 1 to a primary device controller,e.g. to the controller of an automated cash dispenser, is illustrated inthe drawings on a simplified basis in the form of a general signal anddata interface 12 for communicating with and transmitting informationfrom the magnetic card 3. In order to retain clarity in the drawings,the data sink is not illustrated.

The noise field generator 16 may also have various control inputs andcontrol outputs. For example, the noise field generator 16 may haveinput and output interfaces for controlling activation and deactivationof the noise field 18, for triggering an initial calibration duringwhich the coefficients of the signal transmission model and signalbehaviour are stored, for triggering a reset of the hardware and/or forsignalling an unacceptably high variance between the stored signal model(desired state) and the actual transmission conditions (actual state)which occur. The latter interface of the noise field generator 16 istherefore able to provide an indication of any unauthorised manipulationof the reading device 1.

The functions of the described inputs and outputs may also be handled bya more complex communication interface, which is provided as a means ofcommunicating with a primary controller computer. A more complexinterface might be a serial RS232 or RS485 interface, an Ethernetinterface or a USB-interface, for example.

FIG. 4 illustrates an advantageous embodiment of the noise fieldgenerator 16 proposed by the invention, by means of which at least asecond noise field coil 22 is provided in addition to the first fieldcoil 17, to which a second noise control signal not correlated with thefirst noise control signal is applied. This improves security againstmanipulation of the reading device 1 still further.

In this instance, the noise field generator 16 is an integral componentof the central evaluation and control circuit 11 of the reading device1. The output or sum signal of the legitimate or authorised magneticfield reading head 10 is suppressed in the digital signal processor unit21 (DSP), i.e. the elements correlated with the two noise signals arecomputed out. The signal suppressed in this manner, i.e. thereconstructed wanted signal of the magnetic field reading head 10, isthen directly decoded in an adequate manner by the digital signalprocessor unit 21 (DSP) and the extracted data is forwarded to a primarydevice controller, in particular via the signal and data interface 12.In this instance, the digital signal processor unit 21 (DSP) alsoassumes control of the drive or conveyor rollers 7, 7′ of the readingdevice 1 and activation of other components which might be provided,although these are not illustrated, such as a controllable closurescreen for the card reader opening, or the evaluation of various sensorsused to detect the position of an inserted magnetic card 3.

FIG. 5 is a block diagram illustrating the digital signal processingwhich takes place in the digital signal processor unit 21 for arelatively simple form of the noise field generator 16, for example forimplementing the invention based on a reading device 1 of the typeillustrated in FIG. 3.

The output point for generating the stochastic noise control signal is adigital pseudo-random number generator 23. This generator generates atleast pseudo-type random numbers. The sequence of random numbersgenerated by the pseudo-random number generator 23 corresponds at leastapproximately to a white noise with a largely uniform spectral powerdensity in the entire discrete frequency range of the digital scanningsystem.

The white noise sequence of the pseudo-random number generator 23 ispreferably limited by means of a digital band pass filter 24 to afrequency band which usually contains at least a part of thosefrequencies which occur in the wanted signal of the magnetic fieldreading head 10 when the magnetic card 3 is being read—FIG. 3. The powerand bandwidth of the noise control signal are concentrated on thosefrequencies which are essential to distorting the signal in the foreignor illegal magnetic field reading head 14—FIG. 3—and which can also beeliminated by means of simple band pass filtering without also removingthe elements of the wanted signal. The output sequence limited bybandwidth is forwarded to a DA convertor, not illustrated, where it isconverted into an analogue noise control signal for activating the noisefield coil 17—FIG. 3.

The same random number sequence of the pseudo-random number generator 23or—as indicated by broken lines—the output signal of the band passfilter 24 is also forwarded to a signal-based model 25, in particular adigital model filter 25 a. The digital model filter 25 a illustrated inthis instance is an FIR filter of the standard type. Details of thedesign, operation and properties of such FIR filters may be found in therelevant background literature. The coefficients of the model filter 25a are selected so that the entire signal transmission behaviour of thereal route from the pseudo-random number generator 23 via the band passfilter 24, noise field coil 17 and magnetic field reading head 10 isimitated in terms of signals. The coefficients of the model filter 25 adescribe the signal transmission behaviour of the entire trans-missionroute between the pseudo-random number generator 23 and fictitioussummation point 26 disposed between the signal of the magnetic fieldcoil 10—FIG. 3—and the output signal of the digital model filter 25 a.The coefficients of the model filter 25 a preferably characterise theentire signal transmission behaviour within the route between thepseudo-random number generator 23, band pass filter 24 and the elementsof the DA convertor 19′ illustrated in FIG. 3 by way of example,amplifier and adaptation stage 20′, noise field coil 17, magnetic fieldreading head 10, amplifier and adaptation stage 20 and the AD convertor19 back to the summation point 26. As explained above, other componentswhich determine or affect signal transmission behaviour may also beprovided within this signal transmission route between the pseudo-randomnumber generator 23 and a return path 27 running from the magnetic fieldreading head 10—FIG. 3—to the summation point 26. The other influencingfactors within this signal transmission route are best provided by thefilter coefficients and the model filter 25 a. The essential factor isthat the filter coefficients form a signal-based model 25 which imitatesthe actual signal transmission behaviour across the signal transmissionroute described above sufficiently accurately. In the case of thissimple basic form of noise field generator 16, the filter coefficientsare set up on a one-off and fixed basis, in particular a factory setup.The filter coefficients can be determined at the factory as soon as thecomplete reading device 1 has been assembled and can be initiated bymeans of a calibration routine, for example.

At the summation point 26, the computed sequence of the noise fieldinfluence is subtracted from the real output or sum signal of themagnetic field reading head 10 or from its digitized sequence ofscanning values. The real signal of the magnetic field reading head10—FIG. 3—is then directed via the symbolic return path 27 to themodel-type summation point 26. At the summation point 26, the distortedelement in the output or sum signal is eliminated from the magneticfield reading head 10 and a non-distorted or suppressed wanted signal isreconstructed for ongoing processing. This suppressed wanted signal isthen applied to a summation path 28 of the summation point 26.

The sequences and connections described above should be understood asbeing based on a model. They are implementation by thesoftware-controlled, programmable signal processor unit 21 (DSP). Inparticular, the signal-based model 25 described above is run by means ofthe signal processor unit 21 (DSP).

FIG. 6 illustrates a more complex variant of the signal processing ofthe noise field generator 16 by means of which, by contrast with thebasic variant illustrated in FIG. 5, the model filter 25 a can beadapted to the real transmission behaviour subsequently or constantlyand/or adaptation can be activated as and when necessary. A programmemodule containing an appropriate adaptation algorithm 28 is thereforerun in the signal processor software. A known adaptation algorithm 28 isthe so-called LMS algorithm (Least Mean Square)—for more details, seethe background literature by Widrow Stearns. The adaptation may takeplace both in time and using the Fast Fourier Transformation (FFT) inthe frequency range.

The fact that the filter coefficients of the model filter 25 a areconstantly adapted by means of the adaptation algorithm 28 enables ahigher quality to be obtained in terms of reconstructing thenon-distorted signal sequence because even small changes which occur inthe real trans-mission behaviour, such as temperature-inducedfluctuations or changes due to ageing, can be comprehensivelycompensated. Another advantage of constant adaptation is the possibilityof being able to compare the filter parameters for the currenttransmission behaviour with a previously stored reference status whichmeans that variances due to tampering can be detected. Such variancescaused by tampering can then be signalled to an authorised point or tothe user of the reading device 1, and the digital signal processor unit21 can initiate or generate alarm-and/or error messages, for example.Alternatively or in combination with this, the anti-tampering systemincorporating the noise field generator 16 may cause the reading device1 to be locked or placed out of service or may place the entireautomated machine equipped with the reading device 1 out of service.

To enable manipulative actions on the reading device 1 to be reliablydetected, it may be of advantage if, instead of the band pass filter 24,a filter is used to optimise the power of the noise control signal whichalso has a specific minimum power density outside the actual noisefrequency band (shaping filter) but which may be below that of theactual noise control signal. This improves the possibility of being ableto detect changes in the transmission behaviour of the real route andmeets the digital requirements for constant adaptation of the modelfilter 25 a.

By using an appropriate control command system or a control line 29, acalibration routine can be initiated if necessary, i.e. as a function ofthe process and/or controlled by the user, by means of which the digitalfilter coefficients of the model filter 25 a can be adapted to thetransmission behaviour of the real route and can then be stored in anon-volatile memory 30. The stored parameters are used both forinitialising the model filter 25 a after switching on the supply voltageand as a reference with respect to a non-distorted or non-manipulatedstate of the reading device 1. However, initiation of a calibration oradaptation routine for the model filter 25 a may also be controlled on atimed basis. The essential aspect is that as a result of this adaptivemodel filter 25 a, the signal-based model 25 can be adapted so thatlong-term or creeping or even small changes in the signal transmissionbehaviour which are not attributable to tampering or defects can betaken into account as effectively as possible during the preferablycomputerised compensation of the noise field effect.

FIG. 7 illustrates an even more sophisticated variant of the signalprocessing of the noise field generator 16 and the signal-based model25, in particular for a reading device 1 of the type illustrated in FIG.4. By contrast with the variant illustrated in FIG. 6, twonon-correlated noise signal sequences are generated as a means ofactivating two noise field coils 17, 22—FIG. 4. This results in atwo-channel noise field, as it were. A separate model filter 25 a, 25 a′is provided for each of the two noise channels, which model the effectof the respective noise signal on den magnetic field reading head 10 ofthe reading device 1. As in FIG. 6, the model filters 25 a, 25 a′ may bebased on an adaptive design and thus adapt on a long-term basis tochanging transmission conditions. The functional elements or componentsof the digital signal processor unit 21 that are respectively duplicatedor used more than once are denoted by the relevant reference numberprefixed with an additional apostrophe.

As also illustrated in FIG. 7, the wanted signal from the legitimatemagnetic field reading head 10 of the reading device 1 is decoded by thedigital signal processor unit 21. To this end, the signal processor unit21 runs an evaluation unit 31 operated by software. As illustrated bythe block diagram shown in FIG. 7, the drive for the device conveyingthe card inside the reading device 1—FIG. 4—is also activated by thesignal processor unit 21, in particular by a drive controller 32operated by it. Furthermore, at least the magnetically stored card data,in particular at least the relevant or requisite parts of this data, areforwarded via a co-operating interface 33 to a primary devicecontroller.

Advantageous features of the method and operating modes of the inventionwill be described below with reference to the embodiments illustrated inFIGS. 3-7. Parts that are the same in the different embodiments aredenoted by the same reference numbers in these drawings illustrating themethod and configuration of the invention.

As with the embodiments described above as examples, a noise fieldgenerator 16 is provided, which co-operates with and is coupled with asignal-based model 25. By means of this signal-based model 25, thesignal transmission behaviour from the noise field coil 17 to theinternal magnetic field reading head 10 of the reading device 1 iscopied and described. Taking account of the signal-based model 25, theeffect of the noise field 18 on the output signal of the magnetic fieldreading head 10 and the characteristic of the noise field 18 iscalculated. In particular, the output or sum signal of the magneticfield reading head 10 made up of the wanted signal from the card-shapeddata carrier 2 and the noise control signal or noise field 18 iscorrected by subtracting the calculated effect of the noise field. Theeffect of the noise field 18 on the magnetic field reading head 10 istherefore completely or almost completely compensated. After subtractingthe calculated effect of the noise field, the remaining signal or wantedsignal contains only those elements that were generated due to themagnetic stripe 4 of a magnetic card 3 being moved past the magneticfield reading head 10. In other words, the calculated signal correspondsto a wanted signal as it would have been detected without the effect ofthe additional noise field 18.

The signal-based model 25 for calculating the effect of the noise fieldin advance is preferably implemented in the form of the digital modelfilter 25 a respectively 25 a′, which may be provided in the form of anFIR filter in particular. The digital model filter 25 a respectively 25a′ is expediently run by software and implemented by means of the signalprocessor unit 21. Such a model filter 25 a, 25 a′ has a set of filtercoefficients, by means of which the frequency and phase response of thefilter can be set sufficiently accurately. The FIR (finite impulseresponse) filter is therefore preferably a digitally operated filter. Inprinciple, however, a suitable signal-based model 25 could also be setup on the basis of analogue technology and used for the purposes of theinvention. In other words, the main parts of the described signalprocessing could also be run using analogue technology.

The specified features offer a whole range of major improvements andthese features constitute a starting point for various advantageousembodiments. First of all, the noise field 18 does not have to bedeactivated whilst the magnetic card 3 is passing through the internalor authorised magnetic field reading head 10 of the reading device 1because the effect of the noise field 18 is compensated by signals atevery instant and the non-distorted wanted signal originating from thedata of the magnetic stripe 4 can be reconstructed by computer. Themagnetic noise field 18 can therefore also be used with reading devices1 of a relatively short design—by reference to the direction in whichthe magnetic card 3 is inserted. In other words, the described noisefield generator 16 can also be used with reading devices 1 in which thecard data is already being read whilst a part of the magnetic card 3 isstill protruding out from the reading device 1 and is thus stillaccessible to a magnetic field reading head 14 fitted for fraudulentpurposes or interception. The noise field generator 16 can thereforealso be used with reading devices 1 of a short design and remainconstantly activated and may remain active whilst the magneticallyencoded data of the magnetic card 3 is being read. The fraudulentlyfitted magnetic field reading head 14 is therefore subjected to thenoise field 18 at every relevant instant without there being anypossibility of the signal-based compensation of the distorted partgetting into the output signal of the magnetic field reading head 14fitted with criminal intent.

By means of the signal-based model 25, the effect of the noise field canbe calculated for every active characteristic of the noise field 18 andfor every characteristic of the noise control signal supplied to thenoise field coil 17. By contrast with the system known from the priorart where a noise field generator which generates a periodic noisesignal is used, the system proposed by the invention also enables astochastic, i.e. random, noise control signal or noise field 18 to beused. Whereas the effect of a periodic noise signal on the illegallyfitted magnetic field reading head 14 can be subsequently filtered outrelatively easily and the intact signal information reconstructed, usinga quasi-random noise control signal means that it is no longer possibleto reconstruct the intact signal elements or wanted signal elements fromthe signal of the additional or fraudulently fitted magnetic fieldreading head 14.

Another decisive advantage of the solution proposed by the inventionusing the signal-based model 25 resides in the fact that the magneticfield lines and hence the transmission behaviour of the noise field coil17 at the magnetic field reading head 10 of the reading device 1 ischanged by the manipulative fitting, removal or altering of magneticallyand/or electrically conductive parts within the influencing range of thenoise field coil 17. At the same time, however, a comparison variablefor the original or desired state is available with the signal-basedmodel 25. This means that electrically or magnetically conductive partsfitted in the region of the card reader opening for fraudulent purposesor modified or removed from this region and which were previouslyadapted to the signal-based model 25 no longer match the transmissionconditions actually occurring. If a magnetic card 3 is not being read ora magnetic card 3 is not being inserted, the signal of the magneticfield reading head 10 must be practically zero in the non-manipulatedstate once the effect of the noise field has been compensated. If, onthe other hand, the card reader opening has been tampered with in themanner described above, the changed, actual effect of the noise fieldcan no longer be completely compensated by means of the signal-basedmodel 25 and at least a certain amount of the effect of the noise fieldis present even after compensation or filtering out. With effect from acertain degree, this remaining amount of influence can be evaluated asan indication that tampering has taken place and the reading device 1 orthe automated machine equipped with it can then be placed out of serviceand/or an alarm triggered. In view of the fact that the signal-basedmodel 25 is used, it is also no longer possible to eliminate the effectof the noise field coil 17 without being detected, for example byapplying magnetic screening or by destroying the noise field coil 17,for example by boring through the front plate of the reading device 1,nor is it possible to weaken or eliminate the effect of the noise fieldcoil 17 by inserting tools through the slot of the reading device 1 tomove the noise field coil 17. Each of these acts of tampering causes avariance in the real transmission behaviour from the signal-based model25 so that system critical or fraudulent manipulations can beautomatically detected. The same also applies in the case of a simpledefect, which eliminates or changes the effect of the noise field coil17. Even a defect caused by wear and tear due to age or signs of wear onthe magnetic field reading head 10 of the reading device 1 can thereforebe automatically detected and reported by incorporating the signal-basedmodel 25 in the reading device 1.

As an alternative to using the output signal of the magnetic fieldreading head 10 as a means of monitoring the function and state of thenoise field 18, it would also be possible to use the signal from asensor coil, although this is not illustrated, which is provided solelyfor the purpose of monitoring the noise field 18 and does not otherwisedetect any other wanted signal. Detection of the non-manipulatedoriginal state and then any subsequent manipulation will then take placein exactly the same way as with the output or sum signal of the magneticfield reading head 10, but without detecting and re-processing areconstructed wanted signal.

The explanations and descriptions given in this document relateprimarily to reading devices 1 based on the type involving insertion inthe reader, i.e. reading devices 1 with a motorised drive forautomatically drawing in and conveying an inserted magnetic card 3.However, the invention is equally suitable for other different designsof magnetic card readers currently in use, such as manual swipe readersor readers where the card is simply inserted.

Advantageous features, embodiments and variants of the invention will bedescribed below. Amongst others, it is of advantage to implement thedescribed features using the signal processor unit 21. Using such asignal processor unit 21, a broadband, stochastic, in particularpseudo-random noise control signal can be computed, amongst otherthings. The noise control signal constitutes coloured noise and afiltered and hence spectrally limited noise is generated by a band passfilter 24, which is firstly generated by means of the pseudo-randomnumber generator 23 illustrated in FIG. 5 and then filtered by a bandpass filter 24 as illustrated in the diagrams of FIG. 3 and output viathe DA convertor 19′ and amplifier and adaptation stage 20′ in order toactivate the noise field coil 17. The output or sum signal of themagnetic field reading head 10 suppressed by the noise control signal oraffected by the noise field 18 is also forwarded via the amplifier andadaptation stage 20 to the AD convertor 19 and then applied to theprocessor core or signal processor of the signal processor unit 21. Inthe signal processor unit 21, the signal-based model 25—FIG. 5, 6, 7—forthe route described above is reproduced in the form of a digital modelfilter 25 a, for example in the manner of an FIR filter. The modelfilter 25 a delivers at its output the same or virtually the same signalsequence as that of the AD convertor 19—FIG. 3—due to the output signalof the magnetic field reading head 10 if no magnetic card 3 is beingread and the noise field 18 is merely acting on the magnetic fieldreading head 10. The computed noise signal is also subtracted from theoutput or sum signal of the magnetic field reading head 10 in the signalprocessor unit 21 and the remaining or resultant signal is eitherconverted by via a DA convertor 19″—FIG. 3—back into an analogue signaland passed through the original evaluation and control circuit 11 fordecoding the card data (FIG. 3) or this decoding takes place in thesignal processor unit 21 already with the aid of appropriate algorithmsand a software module (FIG. 4). The essential aspect is that the effectof the noise field 18 of the noise field coil 17 on the output or sumsignal of the magnetic field reading head 10 is compensated or filteredout or the wanted signal is selectively filtered out of the output orsum signal of the authorised magnetic field reading head 10. Evaluationor subsequent processing of the wanted signal may be run in the readingdevice 1 or in peripheral electronic units.

To this end, the noise field generator 16 contains the signal-basedmodel 25, which is configured to imitate the effect of the noise field18 on the output or sum signal of the authorised magnetic field readinghead 10. This model-based imitation is used to compensate the effect ofthe noise field 18 on the output or sum signal of the authorisedmagnetic field reading head 10 and hence reconstruct a wanted signalfrom the output or sum signal of the authorised magnetic field readinghead 10 depending on the inserted card-shaped data carrier 2.

It is of advantage if the sampling rate and the processing rate of thediscrete scanning system or signal processing unit described above aremore than twice as high as the highest frequency elements of the wantedsignal in the signal of the magnetic field reading head 10 when amagnetic data carrier 2 is being read. This ensures that the informationcontained in the wanted signal is fully and unambiguously detected.

It is of advantage if the model filter 25 a is based on an adaptivedesign and algorithms or software modules are run in the signalprocessor unit 21, by means of which the filter coefficients of themodel filter 25 a are automatically adapted at least once in acalibration routine so that the transmission behaviour corresponds tothe way in which the signal-based model 25 affects the transmissionbehaviour of the real signal path across the noise field coil 17. Thefilter coefficients determined during the calibration routine arepreferably stored in a non-volatile memory 30—FIG. 6—so that there is noneed for another calibration routine when the noise field generator 16is switched on again. The fact that the filter coefficients are storedin memory means that a set of reference coefficients is available whichdescribe the transmission behaviour of the original and non-manipulatedstate of the reading device 1. Various algorithms and methods, some ofwhich have been known from the prior art for many years, may be used todetermine the appropriate filter coefficients such as the Least MeanSquare algorithm (LMS algorithm).

The model filter 25 a is adapted to an individual device, which meansthat there is no need to use a signal-based model 25 that is fixed andalways remains the same for all types of device or all reading devices1. The fact that the effect of the signal-based model 25 is adapted toan individual device in this manner advantageously means that problemsare avoided or at least significantly reduced during operation of thereading device 1, in particular due to component or manufacturingtolerances as well as varying effects attributable to differentinstallation situations.

It is also of advantage if, after an initial calibration routine, thedigital model filter 25 a is also adapted at a slow adaptation speed,i.e. the filter coefficients of the signal-based model 25 are adapted toa slowly changing transmission behaviour. Even without tampering, slightchanges can occur in transmission behaviour, for example due totemperature-induced or age-related changes of component variables.Running a continuous adaptation of the model filter 25 a ensures thatthe effect of the noise field on the magnetic field reading head 10 ofthe reading device 1 is optimally compensated even in the event ofslight changes in transmission behaviour. In spite of the continuous orperiodic adaptation, it is of advantage to provide an initialcalibration routine whereby the model parameters for the transmissionbehaviour in the original state of the device are determined and storedon a non-volatile basis. These stored model parameters are used on theone hand as power-on start-up values for the signal-based model 25 sothat the noise field compensation also operates sufficiently effectivelyimmediately after switching the reading device 1 on. On the other hand,the stored model parameters can be used as comparison values forevaluating the presence of tampering or defects of the reading device 1.This being the case, it is preferable if it is not the remaining, nolonger fully compensatable noise signal that is used as a characteristicfor tampering or a defect but rather the variance of the continuouslycalibrated model parameters from the originally determined and storedmodel parameters.

Based on one advantageous embodiment, the output signal of theauthorised magnetic field reading head 10, corrected as regards theeffect of the noise field, is constantly monitored during those phaseswhen no magnetic data carrier 2 is being inserted in the reading device1 to ascertain whether a specific total or spectral power is beingexceeded. If this is the case, an appropriate status or error message ismade available to a primary device controller because this is anindication of tampering.

Based on another advantageous embodiment, the broadband stochastic noisecontrol signal is limited by means of a digital filter, in particular bymeans of a band pass filter 24, to a bandwidth which contains at least apart of the bandwidth of the wanted signal as a result of the datarecorded on the magnetic card 3 and a specific adjoining frequencyrange. Limiting the bandwidth to the range typical for the wanted signalreduces the total power of the noise control signal necessary or to beapplied as a ratio of its intensity and effect in the frequency range ofthe wanted signal and, conversely, a stronger effect can be achieved inthe spectral range of the wanted signal with the same output power sothat the proportion of the active noise control signal compared with theproportion of the wanted signal can be increased. The dimensioning ofthe amplifier and adaptation stage 20′—FIG. 3—and the dimensioning ofthe noise field coil 17 can, conversely, be selected for a lower totalpower, which usually results in a more compact design and moreenergy-efficient operation of the noise field generator 16 and readingdevice 1.

Based on one advantageous embodiment, a deterministic signal componentmay additionally be superimposed on the stochastic noise control signal.This deterministic signal component is similar to essential propertiesof the wanted signal when a magnetic card 3 is being read.

However, the deterministic signal component ultimately does notrepresent valid data. This feature makes it even more difficult toreconstruct the intact signal and determine the wanted signal from thesignal of the illegally fitted magnetic field reading head 14. Thisadditional signal component may also be variable, in particular containrandom characteristics, which make it yet more difficult to distinguishor separate the signal originating from the magnetic card 3 by signalprocessing.

The advantageous embodiment illustrated in FIG. 4 is based on the use ofat least one other noise field coil 22, which is spaced at a distanceapart from the first noise field coil 17 or is oriented differently interms of its magnetic field or has different magnetic field geometry.This second noise field coil 22 is supplied with a second, likewisestochastic, noise control signal which is linearly independent of thenoise signal for the first noise field coil 17. This means that thenoise control signals for the different noise field coils 17, 22 are notrespectively correlated with one another. To a certain extent, thisresults in a multi-channel noise field 18, as a result of which thepossibility of reconstructing the relevant wanted signal representingthe card data from the suppressed signal of an illegally fitted magneticfield reading head 14 is even more significantly reduced, therebyfurther improving security against tampering.

Based on another advantageous embodiment, the anti-tampering system ofthe reading device 1 described above and an automated machine equippedwith it may also be designed so that the insertion orifice 6 of thereading device 1 is automatically locked if tampering is detected, thenoise field generator 16 is not functioning or the signal processingpart of the anti-tampering system is inactive.

The term “signals” used above in the context of the digital scanningsystem, i.e. in connection with the digital signal processor unit 21,should primarily be understood as meaning a sequence of digital scanningvalues.

FIG. 8 illustrates an advantageous embodiment of the reading device 1 oranti-tampering system, the same reference numbers being used to denotesame parts already described above, and the descriptions given aboveapply literally to those same parts denoted by the same referencenumbers. The diagram in FIG. 8 illustrates an embodiment which may beused with the embodiment illustrated in FIG. 4, and it would naturallyalso be possible for this embodiment to be used with the variantillustrated in FIG. 3.

As a result of this advantageous embodiment, the reconstructed wantedsignal is encrypted in the reading device 1 or by means of theevaluation and control device 11. A standard encryption and decryptionalgorithm 34 is used for encrypting and/or decrypting signals and data.A suitable encryption and decryption method might be DES, TripleDES, RSAor similar, for example.

Encrypted accordingly, the wanted signal, which is based on themagnetically encoded data of an inserted data carrier 2, is thenforwarded or transmitted across the data interface 12 or across the atleast one status and signal wire 13 to a primary or peripheralelectronic unit, for example an automated service machine. In thisauthorised electronic unit, the received encrypted signal is firstlydecrypted by means of an adequate decryption and encryption algorithm 35so that the wanted signal can then be evaluated and further processed toobtain its data.

It is of practical advantage if the wanted signal from the data carrier2 is decrypted to obtain its data by means of the signal processor unit21, which is also programmed to compensate or filter out the effect ofthe noise field 18 of the noise field coil 17. Similarly, encryption ispreferably handled by the computer unit of the peripheral unit, which isusually provided in the form of an industrial PC with co-operatingsoftware.

In a similar way, when writing data to the magnetic stripe 4, theencryption may be run in the industrial PC by means of the decryptionand encryption algorithm 35 and decryption by means of the encryptionand decryption algorithm 34 may be run by the evaluation and controldevice 11, in particular by the digital signal processor unit 21.

As a result of this advantageous embodiment, even if there have beenattempts to tamper with the interior of the reading device 1, it will nolonger be possible to obtain usable wanted signals or data from the datacarrier 2. If using the features described above, it may not benecessary to encapsulate the reading device 1 with relatively complexand expensive features in order to protect it against unauthorisedtampering in many cases. The only other area which is relevant tosecurity and might require protection is on a chip or a small area of afew chips inside the reading device 1. This enables comprehensivesecurity to be obtained against fraudulent manipulation at relativelylittle cost.

The objective underlying the independent solutions proposed by theinvention may be found in the description.

Above all, the individual embodiments illustrated in FIGS. 3, 4, 5, 6,7, 8 may be construed as independent solutions proposed by the inventionin their own right. The objectives and associated solutions may be foundin the detailed descriptions of these drawings.

LIST OF REFERENCE NUMBERS

-   1. Reading device-   2. Card-shaped data carrier-   3. Magnetic card-   4. Magnetic stripe-   5. Housing-   6. Insertion orifice-   7, 7′. Conveyor roller-   8, 8′. Counter-pressure roller-   9. Guide element-   10. Magnetic field reading head (authorised)-   11. Evaluation and control circuit-   12. Signal and data interface-   13. Status and signal wire-   14. Magnetic field reading head (unauthorised)-   15. Recording apparatus-   16. Interference field generator-   17. Interference field coil-   18. Interference field-   19-19″. AD/DA convertor-   20-20″. Amplifier and adaptation stage-   21. Digital signal processor unit-   22. Interference field coil (second)-   23. Pseudo-random number generator-   24. Band pass filter-   25. Signal-based model-   25 a, 25 a′. Model filter (digital)-   26. Summation point-   27. Return path-   28. Adaptation algorithm-   29. Control line-   30. Memory-   31. Evaluation unit-   32. Drive controller-   33. Interface-   34. Encryption and decryption algorithm-   35. Decryption and encryption algorithm

1. Method of securing a reading device (1) for card-shaped data carriersto prevent unauthorized evaluation or copying of magnetically encodeddata which is detected in the reading device (1) for card-shaped datacarriers (2), whereby a magnetic noise field (18) is generated by meansof a noise field coil (17) disposed in the immediate vicinity of aninsertion orifice (6) for inserting card-shaped data carriers (2) or inthe region of a legitimate or authorized magnetic field reading head(10) of the reading device (1) in order to disrupt or affect with thisnoise field (18) a magnetic field reading head (14) which might havebeen fitted with a view to interception or with fraudulent intent undercertain circumstances whilst the magnetic field of a card-shaped datacarrier (2) is being recorded, comprising operating or disposing atleast one noise field coil (17) so that the authorized magnetic fieldreading head (10) is also affected by the noise field (18) of the noisefield coil (17) as the magnetically encoded data of a card-shaped datacarrier (2) is being read, detecting the output or sum signal of theauthorized magnetic field reading head (10) generated from the wantedsignal of a card-shaped data carrier (2) and from the effects of thenoise field (18), compensating or filtering out the effect of the noisefield (18) of the noise field coil (17) in the output or sum signal ofthe authorized magnetic field reading head (10) or selectively filteringthe wanted signals out of the output or sum signal of the authorizedmagnetic field reading head (10), evaluating or further processing thewanted signal inside the reading device (1) or in peripheral electronicunits.
 2. Method as claimed in claim 1, further comprising computerizedcompensation of the noise effect of the noise field (18) with respect tothe output or sum signal of the authorized magnetic field reading head(10) by means of a signal processor unit (21), whereby a signal-basedmodel (25) is employed by the signal processor unit (21) amongst otherthings, by means of which an effect of a noise control signalrespectively the noise field (18) generated by it on the output or sumsignal of the authorized magnetic field reading head (10) is reproduced.3. Method as claimed in claim 1, further comprising positioning thenoise field coil (17) and/or dimensioning the field intensity or fieldcharacteristic of the noise field coil (17) and/or dimensioning thedetection sensitivity of the authorized respectively legitimate magneticfield reading head (10) so that the noise field (18) of the noise fieldcoil (17) acts on a magnetic field reading head (14) fitted withfraudulent intent, at least when the magnetically encoded data of acard-shaped data carrier (2) is being read and also acts on thelegitimate or authorized magnetic field reading head (10) and affectsits output or sum signal.
 4. Method as claimed in claim 1, furthercomprising generating the noise field (18) from a stochastic electricnoise control signal.
 5. Method as claimed in claim 4, furthercomprising generating the electric noise control signals from a sequenceof pseudo-random scanning values using a pseudo-random number generator(23).
 6. Method as claimed in claim 1, further comprising computing thewanted signal out of the output or sum signal of the magnetic fieldreading head (10) taking account of information about the time sequenceof a stochastic noise control signal or noise field (18).
 7. Method asclaimed in claim 1, further comprising determining the transmissionbehavior or a transmission route from an emitted noise control signal tothe detected output or sum signal on the authorized magnetic fieldreading head (10), and applying the determined transmission behavior inorder to compensate the effect of the noise field (18).
 8. Method asclaimed in claim 1, further comprising determining the discretetransmission behavior of a transmission route from the sequence ofscanning values corresponding to an emitted noise control signal to thesequence of scanning values corresponding to the detected output signalat the authorized magnetic field reading head (10), and applying thedetermined transmission behavior in order to compensate the effect ofthe noise field on a computerized basis.
 9. Method as claimed in claim8, further comprising reproducing the transmission behavior of thetransmission route in a digital model filter (25 a), the effect of whichis described by a set of digital filter coefficients.
 10. Method asclaimed in claim 1, further comprising generating the noise field (18)whilst the magnetically encoded data of a card-shaped data carrier (2)is being detected by the magnetic field reading head (10).
 11. Method asclaimed in claim 1, wherein the output signal of the authorized magneticfield reading head (10) corrected with respect to the effect of thenoise field is monitored continuously during those phases when nocard-shaped data carrier (2) is being inserted in the reading device (1)to ascertain whether a specific total or spectral power is exceeded and,if such is the case, a corresponding status or error message is madeavailable to a primary device controller.
 12. Method as claimed in claim9, wherein the digital model filter (25 a) is adapted to the actualtransmission behavior of the real signal transmission route containingat least the noise field coil (17) and the magnetic field reading head(10) of the reading device (1) during ongoing operation, eitherconstantly or at periodic intervals.
 13. Method as claimed in claim 2,wherein an additional noise control signal is at least periodicallysuperimposed on the noise control signal which, in terms of essentialproperties, is similar to a signal that is obtained as a wanted signalwhen the magnetic stripe of a card-shaped data carrier (2) is read bythe magnetic field reading head (10).
 14. Anti-tampering system for usewith a reading device (1) for the authorized detection of informationmagnetically stored on a card-shaped data carrier (2), which readingdevice (1) comprises a first respective authorized magnetic fieldreading head (10) for scanning a card-shaped data carrier (2) and anevaluation and control circuit (11) for evaluating the output signal ofthe authorized magnetic field reading head (10) and for converting theinformation contained in the output signal into a digital data set, witha noise field generator (16) which generates a magnetic noise field (18)in order to apply noise to a second respective unauthorized magneticfield reading head (14) which might have been fitted in the immediatevicinity of the reading device (1) with fraudulent intent under certaincircumstances, wherein the noise field generator (16) comprises asignal-based model (25) which is configured to copy the effect of thenoise field (18) on the output or sum signal of the authorized magneticfield reading head (10) and this modeled copy is designed to compensatethe effect of the noise field (18) on the output or sum signal of theauthorized magnetic field reading head (10) and thus reconstruct awanted signal dependent on an inserted card-shaped data carrier (2) fromthe output or sum signal of the authorized magnetic field reading head(10).
 15. Anti-tampering system as claimed in claim 14, wherein thenoise field generator (16) comprises at least one noise field coil (17)positioned in the immediate vicinity of an insertion orifice (6) for acard-shaped data carrier (2) which is supplied with a non-periodic,stochastic, in particular pseudo-random, noise control signal. 16.Anti-tampering system as claimed in claim 14, wherein the spectral powerdensity of a noise control signal of the noise field generator (16)within a predefined frequency band containing a part of the standardfrequency range of the wanted signals is significantly higher thanoutside this predefined frequency band when the card-shaped data carrier(2) is being detected.
 17. Anti-tampering system as claimed in claim 14,wherein essential parts needed for processing the signals, in particularthe signal-based model (25) for compensating the effect of the noisefield, are provided in the form of a discrete scanning system comprisingat least one processor, in particular a signal processor unit (21), ananalogue to digital convertor (19) and a digital to analogue convertor(19′).
 18. Anti-tampering system as claimed in claim 14, wherein thesignal-based model (25) is provided in the form of a digital modelfilter (25 a), in particular an FIR filter.
 19. Anti-tampering system asclaimed in claim 14, wherein the noise field generator (16) comprises anon-volatile memory (30) for storing at least one set of filterparameters of a digital model filter (25 a).
 20. Anti-tampering systemas claimed in claim 19, wherein the at least one set of filterparameters defines a model filter (25 a) which copies the transmissionbehavior or transmission characteristic for the noise control signalwhich is emitted via the noise coil (17) and then detected again by theauthorized magnetic field reading head (10) when the reading device (1)is in the non-manipulated, fully functional state.
 21. Anti-tamperingsystem as claimed in claim 20, wherein the model filter (25 a) isadapted during operation, continuously or at regular intervals, and isconstantly adapted to a changing transmission behavior of the realroute, and the at least one set of stored filter parameters is comparedat least on a recurring basis with the set of filter parameters of theadapted model filter (25 a), and the anti-tampering system is configuredto emit a status or error message for a primary device controller in theevent of qualified variances.
 22. Anti-tampering system as claimed inclaim 14, wherein at least one other noise field coil (22) is providedand the noise field coils (17, 22) are disposed in a different spatialarrangement or different orientation or have a different magnetic fieldgeometry and in particular are mounted in the vicinity of an insertionorifice (6) for the card-shaped data carrier (2), and are supplied withstochastic noise control signals that are not correlated with oneanother.
 23. Anti-tampering system as claimed in claim 14, wherein thenoise field coil (17) and the magnetic field reading head (10) arecombined in a common structural unit.
 24. Reading device for theauthorized detection of information magnetically stored on a card-shapeddata carrier (2), wherein the reading device (1) has an anti-tamperingsystem as claimed in claim
 14. 25. Reading device as claimed in claim24, wherein the anti-tampering system is designed to automatically lockan insertion orifice (6) for card-shaped data carriers (2) if amalfunction or manipulation is detected by means of the noise fieldgenerator (16) of the reading device (1).
 26. Automated cash dispenseror access control system, wherein the automated cash dispenser or accesscontrol system has a reading device as claimed in claim
 24. 27. Methodas claimed in claim 1, further comprising encryption of the wantedsignal respectively its data in the reading device (1), by forwarding ofthe encrypted wanted signal respectively its data, and by decryption ofthe wanted signal respectively its data in an authorized, peripherallydisposed electronic unit.
 28. Method as claimed in claim 27, furthercomprising encryption of the wanted signal respectively its data bymeans of a signal processor unit (21), which is also designed tocompensate or filter out the effect of the noise field (18) of the noisefield coil (17).